The trillions of microbes that inhabit your body are collectively called the microbiome.

They outnumber your own cells ten to one and weigh up to twice weight of the average human brain. Most of them live in your gut and intestines, where they help to digest food, synthesise vitamins and ward off infection.

The microbiome has shown that its influence extends far beyond the gut, all the way to the brain.

I’ve written about this in the blog before: One billions reasons probiotics protect your brain, and it looks like the gut-brain topic is hotting up with David Perlmutter author of Grain Brain set to publish a book in April: ‘Brain Maker – the power of gut microbes to heal and protect your brain – for life’. In Brain Maker, Dr. Perlmutter will explain

the potent interplay between intestinal microbes and the brain, describing how the microbiome develops from birth and evolves based on lifestyle choices, how it can become ‘sick’ and how nurturing gut health through a few easy strategies can alter your brain’s destiny for the better.

Not to be outdone, last November members of the Society for Neuroscience (SFN) held a symposium titled Gut Microbes and the Brain: Paradigm Shift in Neuroscience.A summary paper of emerging topics covered in the symposium has been published that claims that

“…the discovery and the explosive progress in the characterisation of the gut microbiome have initiated a paradigm shift in medicine and neuroscience.”

Here is a summary of the symposium discussions:

Gut-Brain signalling

A growing body of preclinical literature has demonstrated there is a complex signaling system between the mind, brain, gut, and its microbiome.

These findings have resulted in speculation that alterations in the gut microbiome may play a pathophysiological role in human brain diseases, including:

“The upstairs and the downstairs need each other to survive. From a distance, it looks like they are living completely separate and they don’t have much to do with one another. But when things start going wrong downstairs that filters on upstairs. It’s the same with the gut and the brain. If there is something wrong with your microbiome, it’s going to filter on upstairs in the brain, too.”

The microbiome is impacted by stress

Psychological and physical stressors alter the composition and metabolism of the gut microbiota. And experimental changes to the gut microbiome can affect emotional behaviour and related brain systems.

For example, when mice are given antibiotics researchers see a decrease in BDNF (a key protein involved in neuronal plasticity and cognition) in the hippocampus (a region involved in emotion, learning and memory).

Tracy Bale, Professor of Neuroscience at the School of Veterinary Medicine at the University of Pennsylvania, and her team have found that stress-induced changes to a mother’s microbiome can be passed to the offspring which in turn might alter the way her baby’s brain develops.

In a recent interview with the Kavli Foundation Bale notes,

“There are key developmental windows when the brain is more vulnerable because it’s setting itself up to respond to the world around it. So, if mom’s microbial ecosystem changes — due to infection, stress or diet, for example — her newborn’s gut microbiome will change too, and that can have a lifetime effect.”

A role for probiotics

A growing body of evidence from rodent studies further supports a role for probiotics. Bifidobacterium and Lactobacillus probiotic treatment shows beneficial effects on anxiety- and depression-like behaviour in rats and mice.

In one human study of chronic fatigue syndrome (another disorder of brain–body interaction) a randomised, double-blind, placebo-controlled trial of a Lactobacillus-containing probiotic decreased anxiety, but not depression symptoms, in the active treatment group. This study, published as a brief report, lacked detail in terms of the reported result and should be interpreted with caution according the SFN symposium attendees.

Probiotics being used widely (and represent a 20 billion dollar industry). Overall, human studies suggest a potential for positive effects on mood, but human work is preliminary and the SFN symposium called for larger, well-designed clinical trials to be conducted.

What’s next for gut-brain research?

Crowd-sourcing fecal samples (yep, The American Gut Project is crowd-sourcing poo!), fecal transplants, mRNA sequencing or proteomics, fMRI … the symposim concluded that it is difficult to predict the trajectory of the next exciting period of discovery.

Will the gut microbiome add paradigm-transforming insights to our existing understanding of human brain function in health and disease, resulting in novel therapies?

Or will it represent an incremental step in understanding the inner workings of our brains?

Certainly, the next few years of research hold the potential of uncovering intriguing connections between gut bacteria and neurological conditions that may possibly impact human health.

Tim Cryan is very enthusiastic,

“We’re right at the dawn of a whole new way of thinking about brain development and brain heath. And the neuroscientific evidence for the role of the microbiome is just getting stronger and stronger at the basic level.”

References

Kavli Foundation. (2015, January 8). Could gut microbes help treat brain disorders? Mounting research tightens their connection with the brain. ScienceDaily. Retrieved January 8, 2015 from www.sciencedaily.com/releases/2015/01/150108125953.htm

The Brain–Gut Axis and Neuropsychiatric Disease: A Paradigm Shift, by Kayt Sukel, December 16, 2014.